Apparatus for flame hardening racks and the like



April 1944- ALKULLMAN ET AL ,346, 23

APPARATUS FOR FLAME HARDENING RACKS AND THE LIKE Original Fi led May 15, 1941 3 Sheets-Sheet 1 ATTORNEYS April 18, 1944. A. KULLMAN EII'AL 2,346,923 APPARATUS FOR FLAME HARDENING RACKS AND THE LIKE Original Filed May 15, 1941 3 Sheets-Sheet 2 "'f ia 2 a R g /Q I IN ENTORS 0 N Q Qaq 4 ,44 ,fl. a] k b w ATTORNEYS April 18, 1944. A. KULLMAN ETAL 2,346,923

APPARATfJs FOR FLAME HARDENING RACKS AND THE LIKE Original Filed May 15, 1941 :5 Sheets-Sheet a Patented Apr. 18, 1944 UNITED s'rATEs APPARATUS FOR FLAME HARDENING BACKS AND THE LIKE Alfred Knllman and Thomas A. Waltz, Cincinnati,

Ohio, assiznors to The American Tool Works ggllnpany, Cincinnati, Ohio, -a corporation of Original application May 15, 1941, Serial No. 393,594. Divided and this application Aulust 22, 1941, Serial No. 407,994

8 Claims. (Cl. 266-) This invention relates to the flame hardening of racks or rack bars for the purpose of hardening the teeth which constitute the rack so as to make them more capable of withstanding wear during usage. Racks 0! the type to which the invention is particularly applicable are those used on lathes and similar machine tools. In a lathe, for example, the rack' is used as means for driving the carriage. This invention contemplates a method and apparatus by which the teeth of the racks may be hardened in order that the teeth may be wear resistant, capable of withstanding any abuse to which they may be subjected, so that more satisfactory performance is obtained from the tool or apparatus of which the rack bars form a part.

The rack bars used on many machine tools or other pieces of equipment, are quite long and of substantial width and thickness. In a lathe, for example, the rack extends substantially the entire length of the lathe bed and may be ten to fifteen feet long and one to two inches thick; sometimes, in very long machines, two such bars are joined, end to end. If such a bar, is heated to ahardening temperature in its entirety, it is distorted and becomes either warped or twisted so badly that it cannot be used. However, it has been determined that the teeth of the'bar can be heated to hardening temperature individually, then cooled and thus hardened, while adjacent portions of the bar are maintained in cool condition, without effecting any appreciable distortion of the bar or causing it to become twisted.

This enables the original shape of the bar to be.

preserved, and yet the desirable hardness and wear resistance be imparted to the rack teeth.

It is conventional in the building of machine tools in which racks are. used to drill pin or screw 1 holes through the base portions of theracks,

then clamp the racks upon the machine to which they are to be mounted, and then drill holes into the machine by using the rack holes previously drilled as guides; this procedure enables the I holesin the machine to be aligned accurately with respect to the holes in the rack. Afterwards, some of the holes in both pieces usually are reamed for the reception of dowel or taper pins. If the base of the rack be hardened, then the holes in it cannot be reamed and special precautions need be taken to obtain the desired alignment. It has beendetermined that .while the teeth'of the rack bars can be hardened in. accordance with the method of the present invention without distortion of the bars, the hard- Za'e has been to provide means tor m" tooth portions only, leaving the base in an unhardened condition and suitable to be drilled and reamed. Thus, the machineability of the base f portionv oi the rack is preserved while the de- 6 sired wear resistance is imparted to the teeth.

- This feature is of particular importance in another respect. Sometimes it is desirable to use short lengths of rack Joined end to end, and when this is the case it is necessary that the 10 teeth at the endwise portion be "mated for preservation' oi the tooth spacing at the juncture.

It the short sections were hardened in their entirety, as some machine builders have done in the past, the metal can be removed to obtain the desired mating" of the teeth only by a slow and tedious grinding operation. The rack bars made in accordance with the present invention can be cut into short is when desirable after the teeth have been hardened simply by means of an ordinary hack saw, and the end surfaces can then be ed to a smooth surface in much less the time than is uired for grind- 'li'he principal object o! the present invention ening the indiual teeth by this technique in amanner which isquicls and 've A further object or the to provide for the hardening ota plurality of so racks ultaneously.

Acetylene gas and oxygen are the mediums used to furnish the heat for the hardening operation; however, these are relatively expensive tor their coation, a further object of the invention has to provide means for automatically cutting of! the discharge of the uthe periods when the flame provided by aes is not being applied-directly to the reel:

so A fr object oi the invention has been to not burned or scorched by the flame.

A still further object of the invention has been to de an apparatus arranged for hardening rack teethone after another serially by means of a torch passing longitudinally of .0 the teeth, that is across the rack bar,.and tov pmvide means for mdexing the torch apparatus relative to the teeth so that each tooth is hardand uniformly throughout its length and uniinvention has been formly with respect to the other teeth of the ening operation readily can be confined to the bar.

Other objects of the invention and further advantages are disclosed in-the detailed specifica tion which follows. The drawings illustrate a preferred embodiment .of apparatus adapted to the practice of the invention. This apparatus is be called. Thus, the protective strips are indicated generally at a in Figure 1, and the racks of the group therebetween at b.

From the point of view of method, therefore, the invention contemplates the flame hardening of an individual tooth of a rack by placing buifer strips at the opposite ends of the tooth,then passing a torch capable of elevating the metal of the tooth to hardening temperature across the tooth and buffer strips with the buffer strips being pressed closely adjacent and preferably in pressure contact with the rack so that the metals at the corners of the rack tooth are kept at a temperature'below that at which they would be particularly useful for hardening the teeth of long rack bars and the like, but it "also may be used. for short or sectional rack lengths. In the apparatus disclosed in the drawings, the rack bars which are to be hardened are held stationarily upon a table and the flame hardening apparatus is advanced serially along the teeth. It will be understood, however, that the invention contemplates the reverse procedure as to both method and machine, that is the stationary mounting of the torch apparatus and serial indexing of the rack teeth relative to it.

In' the drawings:

scorched or burned.

The flame hardening machine which is illustrated in the drawings is comprised of a table upon which the assembly of racks and buffer strips may be supported. This table is indicated generally at I, and it is comprised, most economically, of an inverted channel member Figure 1 is a plan view looking down upon the torch and carriage apparatus and the racks which are to be hardened.

Figure 2 is a side elevation taken sectionally along the line 2-2 of Figure l.

Figure 3 is an elevation looking at the front of the apparatus.

Figure 4 is a sectional detailed view taken on the line 4-4 ofFigure 1.

Figure 5 is a detailed sectional view taken on the line 8-! ofj'igure 2.

It has been determined that if an oxyacetylene flame be passed over an individual tooth of a rack, there is danger that the corners at the ends of the rack tooth will be-burned or scorched; there is greater exposure ofthe metal at these surfaces and less :mass; consequently, the metal is elevated to too high a temperature. r However, we have discovered that if protective racks be placed at opposite sides of the rack which is to be hardened, and if the teeth of all three be aligned, then the two sidewise racks furnish protection against excessiveheat, and the teeth of the central rack are unblemished. The sidewise racks may be used over and over again and, while these sidewise members may be damaged by the heat so as to be unfit for usage as racks, they serve as buil'ers to prevent damage 'to the central member.

In place of a single member protected by the buffer racks, a plurality may be arranged, with I group, and this group is bounded at each side by the protective or bufler racks as they may which is sufficiently long to support the rack group throughout its entire length. The channel member is supported upon a bed 2, which preferably comprises a central trough portion 3, with the table being elevated above the trough and supported thereon by means of the less 4; these may be provided at spaced intervals along the length of the table.

The trough, at each side is provided with rails (and a 'carriage assembly indicated generally at i is arranged to be movable alongthe rails longitudinally of the bed and table.

The carriage i is comprised of a cross mem' ber or cross feed table, indicated generally at I, supported from legs 8-8, and truck members 8 are attached to the bottoms of the legs so as to carry rotatable wheels It for engagement with the side rails 5 of the bed of the apparatus. A pair of wheels is journalled in each truck member, one at each end thereof, and the wheels are grooved as at H to at the rails and thereby guide the carriage. The legs elevate the cross member 1 above the rack assembly so that the carriage is free to travel longitudinally of the for adjustably supporting the torch from the carriage do not form a part of the present inventiomand the details concerning this portion of the apparatus are not, therefore, described in detail. In general, however, the carriage I! is comprised of a base I 4 having a pair of wheels II at each side thereof. These wheels are arranged to track upon rails II which are provided on the cross member I; for instance, in the structure shown in the drawings, cross member I of the cross carriage is comprised of a channel having its flanges extending upwardly, while the legs 8 are fastened to the channel at each end thereof.

Apost n is provided at the backpartof the cross feed carriage, and this post carries the torch adjusting apparatus indicated generally at It. An arm I! extendsfrom the adjusting apparatus to carry a torch column 20, and a distributing head 26 extends below the torch column to carry a pair of torch heads 22. By adjusting the handle 23, the torch may be adjusted longitudinally of the bed and by adjusting the handle 24, the torch heads may be raised and lowered. The knob 25 provides means for tilting the torch head in a plane of revolution parallel to the cross feed table l.

The cross feed carriage I2 is driven by a motor 26 which is controlled through forward and reverse switches 21, a control clutch 28, and a speed controller 29, the latter being arranged for adjustment oi the speed at which the motor drives the torch apparatus across the table. This portion of the equipment, as disclosed in the drawings, is known commercially as the Linde or Airco torch carriage, though other companies make similar equipment.

Oxygen and acetylene are fed to the distributing head 2i through the lines 36 and 3! respectively which are attached to the upper portion of the column 20. From the distributing head, the gases pass through the feed lines 32 and 33 respectively to the torch heads 22.

There are two heads or tips; each preferably is of the multiple jet type and the tips are arranged relative to one another so that the jets of flame impinge upon the opposite sides of a rack tooth being treated.- The jets preferably are water-cooled, and the cooling system is described at a later point in the specification.

In each head or tip, the jets are arranged in tandem with the first jet acting to preheat the metal so that the temperature of it is elevated gradually by the following jets of flame. It is by this method that the heat is confined to the teeth of the rack so as to leave the base portion in a softened condition. It is preferable that the heads or tips be configurated to fit part way down into the groove between the teeth so that the jets of flame may strike the teeth approximately midway between the top of each tooth and its root. In this manner teeth of about .four

permit the torchto be moved transversely over the bed of the machine.

Control valve 34 is mounted on an angle bracket 3! at the forward end of the cross channel l.

- The valve units which it contains are preferably of the reciprocating type, each being mounted in a housing 38 which is' supported upon the bracket 31. handle 40, is pivotally journalled at the upper portion of the valve housing 38, and the lower face of the operating lever is arranged for engagement with the valve stems in such a manner that when the valve stems are depressed, the valves are closed. A tension spring 4! having one end attached to the valve lever and the other end attached to a stud 42 extending from the valve housing, is employed to urge the valve toward closed position.

At the side of the valve lever pivot opposite the tension spring, a cocking mechanism is provided to hold it in open position until it is released, for closure, by a dog extending from the cross feed carriage, and thereby shut off the supply of gas to the torch when the torch has traversed the assembly of racks carried on the table.

In the apparatus disclosed, a clevis arm 43 extends forwardly from the valve housing and pivotally carries. a bell crank or trigger E4. The trigger has a latch arm extending inwardly beyond the pivot, and a notch 56 is provided in this arm for engagement with a latch finger 41 extending downwardly from the levermember 39. A compression spring 48 is installed intermediate the latch arm and the'clevis support 43 so as to urge the arm 45 upwardly into engagement with the latch finger M. The other portion of the bell crank, or trigger, extends to ten pitch can be hadened most conveniently without aiiecting the rack base portion. It is difficult, excepting with teeth of "small size, to obtain the desired elevation of temperature uniformly throughout the tooth by causing a flame to be impinged upon the top of the tooth, and it is also diificut to avoid burning of the metal, as well as to confine the heat, if a large single flame be used. The .preferred torch tips are spaced away from the teeth sufllciently for the blue cone portion of the flame to be spaced slightly away from the metal surface. These features of the present invention concerning particularly the torch head 'or tip are described in more detail and claimed specifically in our copending application. 1

Control valves Oxygen and acetylene are preferred for operation of the torch though other gases may be used.

The gases are supplied to the hardening appapreferably are flexible and take-up loops are' provided at the back part of the cross table to downwardly into the path of travel of the dog member 49 which is fastened, as at 50, to the cross feed carriage l2; there being an aperture 511 in the angle bracket 31 through which the dog 49 is free to pass. As the carriage I2 moves from the back of the machine toward the front across the bed, the dog 49 comes into engagement with the trigger arm 44, swinging it outwardly away from the machine and simultaneously lowering the latch arm 45 against the spring 48.

so that there is no wastage of gas while the feed carriage is being returned and the torch is being located for the heat treatment of the next successive tooth of the assembly of racks.

Ignition of torchflame At the end of each heat treating course of travel, the torch is extinguished. Cross feed carriage I2 then may be returned across the bed, the longitudinal carriage 6 being moved to bring the torch into position for treatment of the next successive tooth. It is then necessary that the torch be relighted, and for this purpose,

a pilot light is employed to accomplish the lighting of the torch automatically after the main control valve 34 has been opened by recocking of that valve through movement of the lever 39 by the handle 40.

The pilot light control apparatus is indicated generally at 52 and it comprises a reciprocating valve 53 and a pilot burner 54 which is con-.

An operating lever 39, having a 55 in order that the burner 53 may project a flame against the torch heads 22.

More specifically, a lever 57: is pivoted in bracket arms 58 extending from the body of the valve, as shown in Figure, 5, with a portion of this lever, at the one side of the pivot, engaging the valve stem 56, and a portion at the other end positioned in the path of travel of an operation dog 59 which is mounted upon the cross feed carriage -2. When the carriage is moved to starting" position, the dog- 59 engages the lever 5?, pushing it backwardly and thereby opening the pilot valve to cause the projection of a jet of flame against the torch heads. As soon as the cross carriage moves the control dog 59 away from the lever 5'5, the valve is operated to cut off the gas supply and thereafter only the pilot light burns.

For pilot lighting purposes, illuminating gas preferably is used and it is supplied to the pilot valve through the feed line 69; this feed line, as illustrated in the drawings, passes to a connection block 6!. The pilot valve itself is supported upon the block M by a pipe stud for communication with the line Ell through the connection block 5i.

Tooth. aligning apparatus pose, the aligning apparatus, indicated gener ally at $2, is utilized.

U-shaped clamp blocks 63-63 are fastened by means of bolts 64 to the downwardly extending flanges at each side of the table I. Pairs of these hanger 65 is then inserted in the slots of the blocks 63, the keeper pins 5's are installed, and the compression screws '52 are turned to press the clamp bar downwardly upon the aligning rods. This operation wedges the rods into the tooth grooves and'brings all of the teeth into exact alignment.

The blocks 63 extend somewhat above the level of the table i and carry clamp screws it at one or at both sides of the table; by turning these screws the racks can be pressed firmly one against the other. Take-up blocks '15 may be employed between the clamp screws 75 and the rack as sembly if the group of racks does not extend across the entire width of the table.

Quenching and cooling The hardening of the teeth is accomplished by elevating the temperature of the metal to a suitable degree, then cooling the metal quickly by means of water or other cooling agent. The coolant is supplied to the machine through two lines. One of these, indicated at it, passes through the connection block 6i and along the cross table to a distributing block ll. From the block 11 the coolant is distributed through the lines l8, l9, and 80; a valve 82 being installed in each line to control the new of coolant. These lines 'l8, T9 and 80 are set relative to the teeth so that with the torch playing a flame upon a given one of the teeth, two of the lines provide coolant to the preceding tooth; that is, the one just hardened by the torch to prevent drawing of the hardened tooth, and the other to the opposite side of the tooth next to be hardened. The coolant flows in the tooth grooves and emerges at the opposite side of the rack assembly blocks are placed at intervals along the table,

.for instance, each twelve to eighteen inches or thereabouts and U-shaped hanger members 65 are provided for each pair of blocks. The hangers have legs 66 extending downwardly and arranged to be inserted in the slots of the U-shaped clamp members, and bores are provided through the blocks and legs so that keeper pins 61 may .be inserted to prevent the hangers from being lifted out of engagement with the blocks. The legs of the hangers are sufllciently long to permit the cross portions of the hangers to reside substantially above the rack assemblies and yet be cleared by the cross table I. P

A clamp bar 68 is arranged beneath the cross portion of each hanger 65, with a. pair of studs 69, headed as at 10, extending upwardly from the clamp bar '68 through bores in the cross member of the hanger. The clamp bar 68 is counterbored appropriately to receive compression springs -1l between the clamp bar and the stud heads so that the springs ll tend to lift the clamp bar 68 upwardly. Two of these lift studs are used, as shown in Figure 2.

.At spaced intervals along the'hanger 65, compression screws 12 are located to press the clamp rods 13 are laid in the tooth grooves. The

thereafter being free to drain into the trough at the bed of the machine.

The second coolant line, indicated at 83, is attached to the distributing head 2 I at the lower end of the torch column 20. The coolant is distributed from this point through two pairs of lines. -One pair indicated at 84 emerges from the back of the distributing head 2| and passes under the block and forwardly to the torch burner heads or tips 22. The lines 84 comprise the main support for the burner tips and should therefore be substantially rigid. The coolant circulates through the tips and is exhausted through a. pair of elbow pipes 85 which direct the coolant out over the racks to the sides of the burner tips. The other pair of coolant lines, indicated at 86, emerges from the top of thedistributing head and extends forwardly and curves together downwardly to directquenching streams of coolant onto the tooth just after it has been heatedto a hardening temperature. The quenching streams may be derived from the exhaust of the cooling stream for the burner tips by pro- Y viding appropriate lines.

Indexing mechanism 89 is fastened to the bracket 88 and comprises a pair of pillow blocks 90 which are bored to re ceive a vertical shaft 9!. A collar 92 is pinned to the shaft 9| intermediate the pair or blocks,

Figure l, the indexing and a compression spring .93, operating against one of the pillow. blocks and the collar, urges the shaft in a downward direction. The bottom of the shaft is arranged to carry a rack segment 94,

and the teeth of this are of the same pitch as those of the rack so the teeth of the segment mesh with the teeth of a rack of the type being treated. Therack segment preferably is removable in order that segments of diflerent size-can be attached to the shaft depending upon the pitch of the racks being treated.

At its upper end, the shaft 9| is provided with a lift pin 95 and a lever 96, pivotally mounted upon. the plate 89, is provided with a fork 91 for engagement around the shaft beneath the lift pin .99. It will be seen that as the operating lever 99 is depressed, as shown in the dot-dash lines in Figure 4, the shaft is lifted to withdraw the teeth of the rack segment from the teeth of a given one of the racks of the assembly, thereby permitting the carriage 6 to be moved longitudinally of the bed of the table.

As shown in the drawings, and particularly mechanism may be arranged to cooperate with a separate indexing rack 99 which is supported along the side of the bed the apparatus and along the racks on in position parallel with the main rack assembly.

This arrangement is desirable because the indexing rack can be isolated from the main group of racks undergoing treatment, and therefore can be kept clean for accurate indexing purposes. Re-

ferring to Figure 1, the bed of the apparatus may be provided with a table extending from the main trough portion located beneath the rack table I. A wall flange 99 may be arranged along respect to a given tooth of'a rack to be treated,

thereafter it is necessary only to lift the indexing segment out of meshing engagement with the rack below it and move the carriage to the next successive indexing station for alignment of the torch head with the next tooth. or the arrangement disclosed, the indexim mechanism may be located above the main rack table I so that the rack which is undergoing treatment also serves as its own index. In this case, it is desirable to have a short piece of rack extend beyond the main assembly at the be of the treatment so as to compensate for the distance between the indem'ng mechanism and the torch head.

I Made of operation the front; that is, toward the control valve as.

with the racks appropriately aligned and clamped upon the table, and the pilot light ignited, the valve 35 may be-cocked to light the torch. At this time, with the coolant being supi as previously described, the cross feed carrlage motor is turned on to move the torch along a rack tooth for the hardeningoperation. when the torch reaches the forward end of the tooth, valve .99 is cut ed by enga ement of the control dog I" with the trigger so as to turn ofii the 5 the carriage returned to starting position. As best illustrated in her I99 may be provided at the terminus of the return run of the carriage 12. The stop member may be fixed .to the rear of the cross channel I, and extend upwardly into the path of travel of a dog llil mounted upon the carriage l2. The carriage is then indexed longitudinally to align the torch with the next successive tooth to behardened and the cycle of operations repeated.

The carriage preferably always is operated between two rack clamps and as the hardening of teeth one after another progresses and the torch is near one of the hangers 65, it may be removed andinserted in the next successive pair of hanger blocks 99 down the bed of the machine while the next succeeding clamp may be moved up to the blocks just behind the carriage.

The clamping of the racks side by side is employed for the purpose of bringing the racks into metal to metal contact so that there will be good dissipation oilheat from one to the other for best cooling purposes. It is in this manner that the scorching and the burning of the sharp edges of the teeth are avoided through the prevention of excessive temperatures at the portions which are most exposed to the torch flame. 0n the other hand, the pressure clamps hold the racks firmly upon the table so that the teeth of all are at a given elevation with respect to the torch flame to provide for uniformity of hardness from tooth to tooth.

This application is divisional of our application Serial No. 393,594, filed May 15, 1941 for Flame hardening of rack bars."

Having described the principles of the present invention and the preferred embodiments of it, we desire to be limited only by the claims which follow:

1. Apparatus for flame hardening the teeth of racks and the like which comprises a bed having a table for supporting a rack" thereon, a carrlage which is movable longitudinally of the ta- In place torch. The motor may then be declutched and 7s ble, means including a torch which is movable upon said carriage transversely of. the table, inotor apparatus for driving said mean across the table, means for feeding gas to said torch inciuding a valve located on said carriage, a dog which is operated in conjunction with said torch supporting means for closing said valve when the torch has been driven across the table. and means for relighting said torch comprising a pilot light. a valve adapted to admit a rush of gas therethrough when the valve is operated, with the pilot being arranged to ignite said rush of gas and thereby direct a Jet of flame toward said torch, and means carried by said torch supporting means for opening said valve when the torch is moved to the opposite side of the table.

2. Apparatus for flame hardening the teeth of racks and the like which comprises a table, a

carriage movable longitudinally of the table,

means including a torch carried by the carriage and arranged to be move transversely of the table, means for supplying combustible gas to the torch, valve means for cutting oifj the supply of gas when the torch has been moved to one side of the table, and means including a pilot light and a dog actuated by movement of said carriage for opening said valve means, the pilot light being arranged for relighting the torch when the torch has been moved to the other side of the table, and the dog actuates said valve means to admit the supply of gas to said torch.

3. Apparatus for flame hardg the teeth of Figure 5, a positive stop memracks and the like which comprises a table adapted to support a rack thereon, a carriage movable longitudinally of the rack and table, a torch supported by said carriage, means for moving the torch transversely of the table whereby a flame provided by the: torch may pass along the teeth of racks supported on the table, a hanger and the like which comprises a bed for support-- ing a plurality of racks thereon, a carriage movable longitudinally of the bed, a torch supported by the carriage, means for moving the torch across the carriage and transversely of the bed, means for clamping a plurality of racks located on the bed, one against the other, an aligning member and means for pressing said aligning member into the tooth grooves of racks located on the bed for aligning the teeth of the racks before they are clamped against one another and also for holding the racks under pressure against 5.'Apparatus for flame hardening the teeth oi racks and the like which comprises a table, a carriage movable longitudinaily'oi the table, a torch movable across the carriage, with the said torch being arranged 'to provide a jet of flame capable oi heating the metal of the teeth of racks located on the table to hardening temperature as the torch is moved transversely of the table, a plurality of clamping means arranged at spaced intervals longitudinally of the table for clamping racks located on the table against one another, and means extending transversely across the table for pressing the aligne racks against thetable.

- 6. Apparatus for flame hardening the teeth of racks and the like comprising a table, a carriage movable longitudinally of the table, a torch movable across the table, with said torch being arranged to provide a jet of flame capable of heating the metal of the teeth .of racks located on the table to hardening temperature as the torch is moved transversely, and means supported from the table and extending transversely across it at opposite sides of said torch, said means including clamp screws for pressing racks located on said table into clamped engagement therewith.

'7. Apparatus for flame hardening the teeth of racks and the like comprising a table, a carriage movable longitudinally of th table, a torch movable across the table, with said torch being, arranged to provide a jet of flame capable of heating the metal 01 the teeth of racks located on the table to hardening temperature as the torch is moved transversely, clamp means extending transversely across the table at spaced intervals longitudinally thereof for pressing racks against the table and additional clamp means for pressing a plurality of racks arranged upon the table in side by side relationship against one another.

8. Apparatus for flame hardening the teeth of racks and the like comprising a table, a caniage movable longitudinally of the table, a torch movby the teeth of the butler racks constitute the terminals of each line of teeth-and prevent the edges of the teeth of the racks being treated from being burned.

THOMAS A. WAL'IZ. 

